also cess-pool, 1670s, the first element perhaps an alteration of cistern, perhaps a shortened form of recess [Klein]; or the whole may be an alteration of suspiral (c.1400), "drainpipe," from Old French sospiral "a vent, air hole," from sospirer "breathe," from Latin suspirare "breathe deep" [Barnhart]. Meaning extended to "tank at the end of the pipe," which would account for a possible folk-etymology change in final syllable.